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<title>GNU libtextstyle: 3. The programmer's perspective</title>

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<hr size="2">
<a name="The-programmer_0027s-view"></a>
<a name="SEC15"></a>
<h1 class="chapter"> <a href="libtextstyle_toc.html#TOC15">3. The programmer's perspective</a> </h1>

<p>As a programmer, enabling styling consists of the following tasks:
</p><ol>
<li>
Define the command-line options and environment variable that the user
can use to control the styling.
</li><li>
Define the CSS classes that the user can use in the CSS file.  Each CSS
class corresponds to a text role; each CSS class can be given a different
styling by the user.
</li><li>
Change the output routines so that they take an &lsquo;<samp>ostream_t</samp>&rsquo; object
as argument instead of a &lsquo;<samp>FILE *</samp>&rsquo;.
</li><li>
Insert paired invocations to <code>styled_ostream_begin_css_class</code>,
<code>styled_ostream_end_css_class</code> around each run of text with a
specific text role.
</li><li>
Link with <code>libtextstyle</code>.  If your package is using GNU autoconf,
you can use the <code>libtextstyle.m4</code> macro from Gnulib.
</li><li>
Prepare a default style file.
</li><li>
Update the documentation of your package.
</li></ol>

<p>The following sections go into more detail.
</p>


<a name="Basic-use"></a>
<a name="SEC16"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC16">3.1 Basic use of libtextstyle</a> </h2>

<p>Source code that makes use of GNU libtextstyle needs an include statement:
</p>
<table><tr><td>&nbsp;</td><td><pre class="smallexample">#include &lt;textstyle.h&gt;
</pre></td></tr></table>

<p>Basic use of GNU libtextstyle consists of statements like these:
</p>
<table><tr><td>&nbsp;</td><td><pre class="smallexample">  styled_ostream_t stream =
    styled_ostream_create (STDOUT_FILENO, &quot;(stdout)&quot;, TTYCTL_AUTO,
                           style_file_name);
  ...
  styled_ostream_begin_use_class (stream, css_class);
  ...
  ostream_write_str (stream, string);
  ...
  styled_ostream_end_use_class (stream, css_class);
  ...
  styled_ostream_free (stream);
</pre></td></tr></table>

<p>Before this snippet, your code needs to determine the name of the style
file to use (<code>style_file_name</code>).  If no styling is desired &ndash; the
precise condition depends on the value of <code>color_mode</code> but also on
your application logic &ndash;, you should set <code>style_file_name</code> to
<code>NULL</code>.
</p>
<p>An object of type <code>styled_ostream_t</code> is allocated.  The function
<code>styled_ostream_create</code> allocates it; the function
<code>styled_ostream_free</code> deallocates it.
</p>
<p>Such <code>styled_ostream_t</code> supports output operations
(<code>ostream_write_str</code>), interleaved with adding and removing CSS
classes.  The CSS class in effect when an output operation is performed
determines, through the style file, the text attributes associated with
that piece of text.
</p>


<a name="Hyperlinks"></a>
<a name="SEC17"></a>
<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC17">3.1.1 Hyperlinks</a> </h3>

<p>Text output may contain hyperlinks.  These hyperlinks are encoded through
an escape sequence, specified at
<a href="https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda">Hyperlinks in terminal emulators</a>.  Currently (as of 2019), they are
displayed only in <code>gnome-terminal</code> version 3.26 or above.  More
terminal emulators will support hyperlinks in the future.  Terminal
emulators which don't support hyperlinks ignore it, except for a few
terminal emulators, for which users may need to disable the hyperlinks
(see <a href="libtextstyle_2.html#SEC9">The environment variable <code>NO_TERM_HYPERLINKS</code></a>) if the heuristic built into
<code>libtextstyle</code> does not already disable them.
</p>
<p>To emit a hyperlink, use code like this:
</p>
<table><tr><td>&nbsp;</td><td><pre class="smallexample">  styled_ostream_t stream = ...
  ...
  /* Start a hyperlink.  */
  styled_ostream_set_hyperlink (stream, url, NULL);
  ...
  /* Emit the anchor text.  This can be styled text.  */
  ostream_write_str (stream, &quot;Click here!&quot;);
  ...
  /* End the current hyperlink.  */
  styled_ostream_set_hyperlink (stream, NULL, NULL);
</pre></td></tr></table>

<p>The anchor text can be styled.  But the hyperlinks themselves cannot be
styled; they behave as implemented by the terminal emulator.
</p>

<a name="Include-files"></a>
<a name="SEC18"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC18">3.2 Include files</a> </h2>

<p>The include file <code>&lt;textstyle.h&gt;</code> declares all facilities defined by
the library.
</p>

<a name="Link-options"></a>
<a name="SEC19"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC19">3.3 Link options</a> </h2>

<p>The library to link with is called <code>libtextstyle</code>, with a
system-dependent suffix.  You link with it though link options of the
form <code>-ltextstyle</code> for a library installed in system locations, or
<code>-L<var>libdir</var> -ltextstyle</code> for a static library installed in other
locations, or <code>-L<var>libdir</var> -ltextstyle -Wl,-rpath,<var>libdir</var></code>
for a shared library installed in other locations (assuming a GCC
compatible compiler and linker and no <code>libtool</code>), or
<code>-L<var>libdir</var> -ltextstyle -R<var>libdir</var></code> for a shared library
installed in other locations (with <code>libtool</code>).  Additionally, the
link options may need to include the dependencies: <code>-lm</code>, and
<code>-lncurses</code> or (on NetBSD) <code>-ltermcap</code> or (on AIX)
<code>-lxcurses</code> or (on HP-UX) <code>-lcurses</code>, and on some systems also
<code>-liconv</code>.
</p>
<p>It is a bit complicated to determine the right link options in a portable
way.  Therefore an Autoconf macro is provided in the file
<code>libtextstyle.m4</code> in Gnulib, that makes this task easier.  Assuming
the build system of your package is based on GNU Autoconf, you invoke it
through <code>gl_LIBTEXTSTYLE</code>.  It searches for an installed
<code>libtextstyle</code>.  If found, it sets and AC_SUBSTs
<code>HAVE_LIBTEXTSTYLE=yes</code> and the <code>LIBTEXTSTYLE</code> and
<code>LTLIBTEXTSTYLE</code> variables, and augments the <code>CPPFLAGS</code>
variable, and #defines <code>HAVE_LIBTEXTSTYLE</code> to 1.  Otherwise, it sets
and AC_SUBSTs <code>HAVE_LIBTEXTSTYLE=no</code> and <code>LIBTEXTSTYLE</code> and
<code>LTLIBTEXTSTYLE</code> to empty.  In link commands that use <code>libtool</code>,
use <code>LTLIBTEXTSTYLE</code>; in link commands that don't use <code>libtool</code>,
use <code>LIBTEXTSTYLE</code>.
</p>
<p>If you use GNU Automake, the proper place to use the link options is
<code><var>program</var>_LDADD</code> for programs and <code><var>library</var>_LIBADD</code>
for libraries.
</p>

<a name="Command_002dline-options"></a>
<a name="SEC20"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC20">3.4 Command-line options</a> </h2>

<p>While you are free to provide any command-line option to enable the
styling of the output, it is good if different GNU programs use the same
command-line options for this purpose.  These options are described in
the sections <a href="libtextstyle_2.html#SEC11">The <code>--color</code> option</a> and <a href="libtextstyle_2.html#SEC12">The <code>--style</code> option</a>.  To
achieve this, use the following API (declared in <code>&lt;textstyle.h&gt;</code>):
</p>
<dl>
<dt><u>Variable:</u> bool <b>color_test_mode</b>
<a name="IDX1"></a>
</dt>
<dd><p>True if a <code>--color</code> option with value <code>test</code> has been seen.
</p></dd></dl>

<dl>
<dt><u>Variable:</u> enum&nbsp;color_option <b>color_mode</b>
<a name="IDX2"></a>
</dt>
<dd><p>Stores the value of the <code>--color</code> option.
</p></dd></dl>

<dl>
<dt><u>Variable:</u> const&nbsp;char&nbsp;* <b>style_file_name</b>
<a name="IDX3"></a>
</dt>
<dd><p>Stores the value of the <code>--style</code> option.
</p></dd></dl>

<p>Note: These variables, like any variables exported from shared libraries,
can only be used in executable code.  You <em>cannot</em> portably use
their address in initializers of global or static variables.  This is a
restriction that is imposed by the Windows, Cygwin, and Android platforms.
</p>
<dl>
<dt><u>Function:</u> bool <b>handle_color_option</b><i> (const&nbsp;char&nbsp;*<var>option</var>)</i>
<a name="IDX4"></a>
</dt>
<dd><p>You invoke this function when, during argument parsing, you have
encountered a <code>--color</code> or <code>--color=...</code> option.  The return
value is an error indicator: <code>true</code> means an invalid option.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>handle_style_option</b><i> (const&nbsp;char&nbsp;*<var>option</var>)</i>
<a name="IDX5"></a>
</dt>
<dd><p>You invoke this function when, during argument parsing, you have
encountered a <code>--style</code> or <code>--style=...</code> option.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>print_color_test</b><i> (void)</i>
<a name="IDX6"></a>
</dt>
<dd><p>Prints a color test page.  You invoke this function after argument
parsing, when the <code>color_test_mode</code> variable is true.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>style_file_prepare</b><i> (const&nbsp;char&nbsp;*<var>style_file_envvar</var>, const&nbsp;char&nbsp;*<var>stylesdir_envvar</var>, const&nbsp;char&nbsp;*<var>stylesdir_after_install</var>, const&nbsp;char&nbsp;*<var>default_style_file</var>)</i>
<a name="IDX7"></a>
</dt>
<dd><p>Assigns a default value to <code>style_file_name</code> if necessary.  You
invoke this function after argument parsing, when <code>color_test_mode</code>
is false.
</p>
<p><code><var>style_file_envvar</var></code> is an environment variable that, when set
to a non-empty value, specifies the style file to use.  This environment
variable is meant to be set by the user.
</p>
<p><code><var>stylesdir_envvar</var></code> is an environment variable that, when set
to a non-empty value, specifies the directory with the style files, or
<code>NULL</code>.  This is necessary for running the testsuite before
&lsquo;<samp>make install</samp>&rsquo;.
</p>
<p><code><var>stylesdir_after_install</var></code> is the directory with the style
files after &lsquo;<samp>make install</samp>&rsquo;.
</p>
<p><code><var>default_style_file</var></code> is the file name of the default style
file, relative to <var>stylesdir</var>.
</p></dd></dl>


<a name="The-output-stream-hierarchy"></a>
<a name="SEC21"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC21">3.5 The output stream hierarchy</a> </h2>

<p>There are various classes of output streams, some of them with styling
support.  These &ldquo;classes&rdquo; are defined in an object-oriented programming
style that resembles C++ or Java, but are actually implemented in C with
a little bit of object orientation syntax.  These definitions are
preprocessed down to C.  As a consequence, GNU libtextstyle is a C
library and does not need to link with the C++ standard library.
</p>
<p>All these classes are declared in <code>&lt;textstyle.h&gt;</code>.
</p>
<p>The base output stream type is &lsquo;<samp>ostream_t</samp>&rsquo;.  It is a pointer type to
a (hidden) implementation type.  Similarly for the subclasses.
</p>
<p>When we say that &lsquo;<samp>some_ostream_t</samp>&rsquo; is a subclass of &lsquo;<samp>ostream_t</samp>&rsquo;,
what we mean is:
</p><ul>
<li>
Every &lsquo;<samp>some_ostream_t</samp>&rsquo; object can be converted to an
&lsquo;<samp>ostream_t</samp>&rsquo;, by virtue of a simple assignment.  No cast is needed.
</li><li>
The opposite conversion, from &lsquo;<samp>ostream_t</samp>&rsquo; to &lsquo;<samp>some_ostream_t</samp>&rsquo;,
can also be performed, provided that the object is actually an instance
of &lsquo;<samp>some_ostream_t</samp>&rsquo;.
</li><li>
Every method &lsquo;<samp>ostream_<var>foobar</var></samp>&rsquo; exists also as a method
&lsquo;<samp>some_ostream_<var>foobar</var></samp>&rsquo; with compatible argument types and a
compatible return type.
</li></ul>



<a name="The-ostream-class"></a>
<a name="SEC22"></a>
<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC22">3.5.1 The abstract <code>ostream</code> class</a> </h3>

<p>The base output stream type is &lsquo;<samp>ostream_t</samp>&rsquo;.
</p>
<p>It has the following methods:
</p>
<dl>
<dt><u>Function:</u> void <b>ostream_write_mem</b><i> (ostream_t&nbsp;<var>stream</var>, const&nbsp;void&nbsp;*<var>data</var>, size_t&nbsp;<var>len</var>)</i>
<a name="IDX8"></a>
</dt>
<dd><p>Writes a sequence of bytes to a stream.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>ostream_write_str</b><i> (ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>string</var>)</i>
<a name="IDX9"></a>
</dt>
<dd><p>Writes a string's contents to a stream.
</p></dd></dl>

<dl>
<dt><u>Function:</u> ptrdiff_t <b>ostream_printf</b><i> (ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>format</var>, ...)</i>
<a name="IDX10"></a>
</dt>
<dt><u>Function:</u> ptrdiff_t <b>ostream_vprintf</b><i> (ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>format</var>, va_list args)</i>
<a name="IDX11"></a>
</dt>
<dd><p>Writes formatted output to a stream.
</p>
<p>These functions return the size of formatted output, or a negative value
in case of an error.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>ostream_flush</b><i> (ostream_t&nbsp;<var>stream</var>, ostream_flush_scope_t&nbsp;<var>scope</var>)</i>
<a name="IDX12"></a>
</dt>
<dd><p>Brings buffered data to its destination.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>ostream_free</b><i> (ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX13"></a>
</dt>
<dd><p>Closes and frees a stream.
</p></dd></dl>


<a name="The-styled_005fostream-class"></a>
<a name="SEC23"></a>
<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC23">3.5.2 The abstract <code>styled_ostream</code> class</a> </h3>

<p>The type for a styled output stream is &lsquo;<samp>styled_ostream_t</samp>&rsquo;.  It is a
subclass of &lsquo;<samp>ostream_t</samp>&rsquo; that adds the following methods:
</p>
<dl>
<dt><u>Function:</u> void <b>styled_ostream_begin_use_class</b><i> (styled_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>classname</var>)</i>
<a name="IDX14"></a>
</dt>
<dd><p>Starts a run of text belonging to <code><var>classname</var></code>.  The
<code><var>classname</var></code> is the name of a CSS class.  It can be chosen
arbitrarily and customized through the CSS file.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>styled_ostream_end_use_class</b><i> (styled_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>classname</var>)</i>
<a name="IDX15"></a>
</dt>
<dd><p>Ends a run of text belonging to <code><var>classname</var></code>.  The
<code>styled_ostream_begin_use_class</code> /
<code>styled_ostream_end_use_class</code> calls must match properly.
</p></dd></dl>

<dl>
<dt><u>Function:</u> const char * <b>styled_ostream_get_hyperlink_ref</b><i> (styled_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX16"></a>
</dt>
<dd><p>Returns the referred URL of the currently set hyperlink, or <code>NULL</code>
if no hyperlink attribute is currently set.
</p>
<p>Note: The returned string is only valid up to the next invocation of
<code>styled_ostream_set_hyperlink</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> const char * <b>styled_ostream_get_hyperlink_id</b><i> (styled_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX17"></a>
</dt>
<dd><p>Returns the id of the currently set hyperlink, or <code>NULL</code> if no
hyperlink attribute is currently set.
</p>
<p>Note: The returned string is only valid up to the next invocation of
<code>styled_ostream_set_hyperlink</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>styled_ostream_set_hyperlink</b><i> (styled_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>ref</var>, const&nbsp;char&nbsp;*<var>id</var>)</i>
<a name="IDX18"></a>
</dt>
<dd><p>Sets or removes a hyperlink attribute.
</p>
<p>To set a hyperlink attribute, pass a non-<code>NULL</code> <var>ref</var>.
<var>ref</var> is an URL; it should be at most 2083 bytes long.  Non-ASCII
characters should be URI-escaped (using the %nn syntax).  <var>id</var> is
an optional identifier.  On terminal output, multiple hyperlinks with
the same <var>id</var> will be highlighted together.  If specified, <var>id</var>
should be at most 250 bytes long.
</p>
<p>To remove a hyperlink attribute, pass <code>NULL</code> for <var>ref</var> and <var>id</var>.
</p>
<p>Hyperlinks don't nest.  That is, a hyperlink attribute is enabled only
up to the next invocation of <code>styled_ostream_set_hyperlink</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>styled_ostream_flush_to_current_style</b><i> (styled_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX19"></a>
</dt>
<dd><p>This function acts like <code>ostream_flush (<var>stream</var>, FLUSH_THIS_STREAM)</code>,
except that it leaves the destination with the current text style enabled,
instead of with the default text style.
</p>
<p>After calling this function, you can output strings without newlines(!) to the
underlying stream, and they will be rendered like strings passed to
<code>ostream_write_mem</code>, <code>ostream_write_str</code>, or <code>ostream_printf</code>.
</p></dd></dl>


<a name="ostream-subclasses-without-styling"></a>
<a name="SEC24"></a>
<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC24">3.5.3 Concrete ostream subclasses without styling</a> </h3>



<a name="The-file_005fostream-class"></a>
<a name="SEC25"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC25">3.5.3.1 The <code>file_ostream</code> class</a> </h4>

<p>The <code>file_ostream</code> class supports output to an <code>&lt;stdio.h&gt;</code>
<code>FILE</code> stream.  Its type is &lsquo;<samp>file_ostream_t</samp>&rsquo;.  It is a subclass
of &lsquo;<samp>ostream_t</samp>&rsquo; that adds no methods.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> file_ostream_t <b>file_ostream_create</b><i> (FILE&nbsp;*<var>fp</var>)</i>
<a name="IDX20"></a>
</dt>
<dd><p>Creates an output stream referring to <code><var>fp</var></code>.
</p>
<p>Note: The resulting stream must be closed before <code><var>fp</var></code> can be
closed.
</p></dd></dl>


<a name="The-fd_005fostream-class"></a>
<a name="SEC26"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC26">3.5.3.2 The <code>fd_ostream</code> class</a> </h4>

<p>The <code>file_ostream</code> class supports output to a file descriptor.  Its
type is &lsquo;<samp>fd_ostream_t</samp>&rsquo;.  It is a subclass of &lsquo;<samp>ostream_t</samp>&rsquo; that
adds no methods.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> fd_ostream_t <b>fd_ostream_create</b><i> (int&nbsp;<var>fd</var>, const&nbsp;char&nbsp;*<var>filename</var>, bool&nbsp;<var>buffered</var>)</i>
<a name="IDX21"></a>
</dt>
<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>.
</p>
<p><code><var>filename</var></code> is used only for error messages.
</p>
<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
closed.
</p></dd></dl>


<a name="The-term_005fostream-class"></a>
<a name="SEC27"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC27">3.5.3.3 The <code>term_ostream</code> class</a> </h4>

<p>The <code>term_ostream</code> class supports output to a file descriptor that
is connected to a terminal emulator or console.  Its type is
&lsquo;<samp>term_ostream_t</samp>&rsquo;.  It is a subclass of &lsquo;<samp>ostream_t</samp>&rsquo;.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> term_ostream_t <b>term_ostream_create</b><i> (int&nbsp;<var>fd</var>, const&nbsp;char&nbsp;*<var>filename</var>, ttyctl_t&nbsp;<var>tty_control</var>)</i>
<a name="IDX22"></a>
</dt>
<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>.
</p>
<p><code><var>filename</var></code> is used only for error messages.
</p>
<p><code><var>tty_control</var></code> specifies the amount of control to take over the
underlying tty.
</p>
<p>The resulting stream will be line-buffered.
</p>
<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
closed.
</p></dd></dl>

<p>The class adds the following methods:
</p>
<dl>
<dt><u>Function:</u> term_color_t <b>term_ostream_rgb_to_color</b><i> (term_ostream_t&nbsp;<var>stream</var>, int&nbsp;<var>red</var>, int&nbsp;<var>green</var>, int&nbsp;<var>blue</var>)</i>
<a name="IDX23"></a>
</dt>
<dd><p>Converts an RGB value
(<code><var>red</var></code>, <code><var>green</var></code>, <code><var>blue</var></code> in [0..255]) to
a color, valid for this stream only.
</p></dd></dl>

<dl>
<dt><u>Function:</u> term_color_t <b>term_ostream_get_color</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX24"></a>
</dt>
<dt><u>Function:</u> void <b>term_ostream_set_color</b><i> (term_ostream_t&nbsp;<var>stream</var>, term_color_t&nbsp;<var>color</var>)</i>
<a name="IDX25"></a>
</dt>
<dd><p>Gets/sets the text color.
</p></dd></dl>

<dl>
<dt><u>Function:</u> term_color_t <b>term_ostream_get_bgcolor</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX26"></a>
</dt>
<dt><u>Function:</u> void <b>term_ostream_set_bgcolor</b><i> (term_ostream_t&nbsp;<var>stream</var>, term_color_t&nbsp;<var>color</var>)</i>
<a name="IDX27"></a>
</dt>
<dd><p>Gets/sets the background color.
</p></dd></dl>

<dl>
<dt><u>Function:</u> term_weight_t <b>term_ostream_get_weight</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX28"></a>
</dt>
<dt><u>Function:</u> void <b>term_ostream_set_weight</b><i> (term_ostream_t&nbsp;<var>stream</var>, term_weight_t&nbsp;<var>weight</var>)</i>
<a name="IDX29"></a>
</dt>
<dd><p>Gets/sets the font weight.
</p></dd></dl>

<dl>
<dt><u>Function:</u> term_posture_t <b>term_ostream_get_posture</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX30"></a>
</dt>
<dt><u>Function:</u> void <b>term_ostream_set_posture</b><i> (term_ostream_t&nbsp;<var>stream</var>, term_posture_t&nbsp;<var>posture</var>)</i>
<a name="IDX31"></a>
</dt>
<dd><p>Gets/sets the font posture.
</p></dd></dl>

<dl>
<dt><u>Function:</u> term_underline_t <b>term_ostream_get_underline</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX32"></a>
</dt>
<dt><u>Function:</u> void <b>term_ostream_set_underline</b><i> (term_ostream_t&nbsp;<var>stream</var>, term_underline_t&nbsp;<var>underline</var>)</i>
<a name="IDX33"></a>
</dt>
<dd><p>Gets/sets the text underline decoration.
</p></dd></dl>

<dl>
<dt><u>Function:</u> const char * <b>term_ostream_get_hyperlink_ref</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX34"></a>
</dt>
<dd><p>Returns the referred URL of the currently set hyperlink, or <code>NULL</code>
if no hyperlink attribute is currently set.
</p>
<p>Note: The returned string is only valid up to the next invocation of
<code>term_ostream_set_hyperlink</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> const char * <b>term_ostream_get_hyperlink_id</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX35"></a>
</dt>
<dd><p>Returns the id of the currently set hyperlink, or <code>NULL</code> if no
hyperlink attribute is currently set.
</p>
<p>Note: The returned string is only valid up to the next invocation of
<code>term_ostream_set_hyperlink</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>term_ostream_set_hyperlink</b><i> (term_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>ref</var>, const&nbsp;char&nbsp;*<var>id</var>)</i>
<a name="IDX36"></a>
</dt>
<dd><p>Sets or removes a hyperlink attribute.
</p>
<p>To set a hyperlink attribute, pass a non-<code>NULL</code> <var>ref</var>.
<var>ref</var> is an URL; it should be at most 2083 bytes long.  Non-ASCII
characters should be URI-escaped (using the %nn syntax).  <var>id</var> is
an optional identifier.  Multiple hyperlinks with the same <var>id</var>
will be highlighted together.  If specified, <var>id</var> should be at most
250 bytes long.
</p>
<p>To remove a hyperlink attribute, pass <code>NULL</code> for <var>ref</var> and <var>id</var>.
</p>
<p>Hyperlinks don't nest.  That is, a hyperlink attribute is enabled only
up to the next invocation of <code>styled_ostream_set_hyperlink</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>term_ostream_flush_to_current_style</b><i> (term_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX37"></a>
</dt>
<dd><p>This function acts like <code>ostream_flush (<var>stream</var>, FLUSH_THIS_STREAM)</code>,
except that it leaves the terminal with the current text attributes enabled,
instead of with the default text attributes.
</p>
<p>After calling this function, you can output strings without newlines(!) to the
underlying file descriptor, and they will be rendered like strings passed to
<code>ostream_write_mem</code>, <code>ostream_write_str</code>, or <code>ostream_printf</code>.
</p></dd></dl>


<a name="The-html_005fostream-class"></a>
<a name="SEC28"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC28">3.5.3.4 The <code>html_ostream</code> class</a> </h4>

<p>The <code>html_ostream</code> class supports output to any destination, in HTML
syntax.  Its type is &lsquo;<samp>html_ostream_t</samp>&rsquo;.  It is a subclass of
&lsquo;<samp>ostream_t</samp>&rsquo;.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> html_ostream_t <b>html_ostream_create</b><i> (ostream_t&nbsp;<var>destination</var>)</i>
<a name="IDX38"></a>
</dt>
<dd><p>Creates an output stream that takes input in the UTF-8 encoding and
writes it in HTML form on <code><var>destination</var></code>.
</p>
<p>This stream produces a sequence of lines.  The caller is responsible for
opening the <code>&lt;body&gt;&lt;html&gt;</code> elements before and for closing them
after the use of this stream.
</p>
<p>Note: The resulting stream must be closed before <code><var>destination</var></code>
can be closed.
</p></dd></dl>

<p>The class adds the following methods:
</p>
<dl>
<dt><u>Function:</u> void <b>html_ostream_begin_span</b><i> (html_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>classname</var>)</i>
<a name="IDX39"></a>
</dt>
<dd><p>Starts a <code>&lt;span class=&quot;<var>classname</var>&quot;&gt;</code> element.  The
<code><var>classname</var></code> is the name of a CSS class.  It can be chosen
arbitrarily and customized through the CSS file.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>html_ostream_end_span</b><i> (html_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>classname</var>)</i>
<a name="IDX40"></a>
</dt>
<dd><p>Ends a <code>&lt;span class=&quot;<var>classname</var>&quot;&gt;</code> element.
</p>
<p>The <code>html_ostream_begin_span</code> / <code>html_ostream_end_span</code> calls
must match properly.
</p></dd></dl>

<dl>
<dt><u>Function:</u> const char * <b>html_ostream_get_hyperlink_ref</b><i> (html_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX41"></a>
</dt>
<dd><p>Returns the referred URL of the currently set hyperlink, or <code>NULL</code>
if no hyperlink attribute is currently set.
</p>
<p>Note: The returned string is only valid up to the next invocation of
<code>html_ostream_set_hyperlink_ref</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>html_ostream_set_hyperlink_ref</b><i> (html_ostream_t&nbsp;<var>stream</var>, const&nbsp;char&nbsp;*<var>ref</var>)</i>
<a name="IDX42"></a>
</dt>
<dd><p>Sets or removes a hyperlink attribute.
</p>
<p>To set a hyperlink attribute, pass a non-<code>NULL</code> <var>ref</var>.
<var>ref</var> is an URL; it should be at most 2083 bytes long.  Non-ASCII
characters should be URI-escaped (using the %nn syntax).
</p>
<p>To remove a hyperlink attribute, pass <code>NULL</code> for <var>ref</var>.
</p>
<p>Hyperlinks don't nest.  That is, a hyperlink attribute is enabled only
up to the next invocation of <code>html_ostream_set_hyperlink_ref</code>.
</p></dd></dl>

<dl>
<dt><u>Function:</u> void <b>html_ostream_flush_to_current_style</b><i> (html_ostream_t&nbsp;<var>stream</var>)</i>
<a name="IDX43"></a>
</dt>
<dd><p>This function acts like <code>ostream_flush (<var>stream</var>, FLUSH_THIS_STREAM)</code>,
except that it leaves the destination with the current text style enabled,
instead of with the default text style.
</p>
<p>After calling this function, you can output strings without newlines(!) to the
underlying stream, and they will be rendered like strings passed to
<code>ostream_write_mem</code>, <code>ostream_write_str</code>, or <code>ostream_printf</code>.
</p></dd></dl>


<a name="The-memory_005fostream-class"></a>
<a name="SEC29"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC29">3.5.3.5 The <code>memory_ostream</code> class</a> </h4>

<p>The <code>memory_ostream</code> class supports output to an in-memory buffer.
Its type is &lsquo;<samp>memory_ostream_t</samp>&rsquo;.  It is a subclass of
&lsquo;<samp>ostream_t</samp>&rsquo;.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> memory_ostream_t <b>memory_ostream_create</b><i> (void)</i>
<a name="IDX44"></a>
</dt>
<dd><p>Creates an output stream that accumulates the output in a memory buffer.
</p></dd></dl>

<p>The class adds the following method:
</p>
<dl>
<dt><u>Function:</u> void <b>memory_ostream_contents</b><i> (memory_ostream_t&nbsp;<var>stream</var>, const&nbsp;void&nbsp;**<var>bufp</var>, size_t&nbsp;*<var>buflenp</var>)</i>
<a name="IDX45"></a>
</dt>
<dd><p>Returns a pointer to the output accumulated so far and its size.  It
stores them in <code>*<var>bufp</var></code> and <code>*<var>buflenp</var></code>, respectively.
</p>
<p>Note: These two return values become invalid when more output is done to
the stream or when the stream is freed.
</p></dd></dl>


<a name="The-iconv_005fostream-class"></a>
<a name="SEC30"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC30">3.5.3.6 The <code>iconv_ostream</code> class</a> </h4>

<p>The <code>iconv_ostream</code> class supports output to any destination.  Its
type is &lsquo;<samp>iconv_ostream_t</samp>&rsquo;.  It is a subclass of &lsquo;<samp>ostream_t</samp>&rsquo;
that adds no methods.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> iconv_ostream_t <b>iconv_ostream_create</b><i> (const&nbsp;char&nbsp;*<var>from_encoding</var>, const&nbsp;char&nbsp;*<var>to_encoding</var>, ostream_t&nbsp;<var>destination</var>)</i>
<a name="IDX46"></a>
</dt>
<dd><p>Creates an output stream that converts from <code><var>from_encoding</var></code> to
<code><var>to_encoding</var></code>, writing the result to <code><var>destination</var></code>.
</p>
<p>Note: The resulting stream must be closed before <code><var>destination</var></code>
can be closed.
</p></dd></dl>


<a name="styled_005fostream-subclasses"></a>
<a name="SEC31"></a>
<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC31">3.5.4 Concrete <code>styled_ostream</code> subclasses</a> </h3>



<a name="The-term_005fstyled_005fostream-class"></a>
<a name="SEC32"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC32">3.5.4.1 The <code>term_styled_ostream</code> class</a> </h4>

<p>The <code>term_styled_ostream</code> class supports styled output to a file
descriptor that is connected to a terminal emulator or console.  Its type
is &lsquo;<samp>term_styled_ostream_t</samp>&rsquo;.  It is a subclass of
&lsquo;<samp>styled_ostream_t</samp>&rsquo;.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> term_styled_ostream_t <b>term_styled_ostream_create</b><i> (int&nbsp;<var>fd</var>, const&nbsp;char&nbsp;*<var>filename</var>, ttyctl_t&nbsp;<var>tty_control</var>, const&nbsp;char&nbsp;*<var>css_filename</var>)</i>
<a name="IDX47"></a>
</dt>
<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>,
styled with the file <code><var>css_filename</var></code>.
</p>
<p><code><var>filename</var></code> is used only for error messages.
</p>
<p><code><var>tty_control</var></code> specifies the amount of control to take over the
underlying tty.
</p>
<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
closed.
</p>
<p>Returns <code>NULL</code> upon failure.
</p></dd></dl>

<p>The following is a variant of this function.  Upon failure, it does not
return <code>NULL</code>; instead, it returns a styled <code>fd_stream</code> on
which the styling operations exist but are no-ops.
</p>
<dl>
<dt><u>Function:</u> styled_ostream_t <b>styled_ostream_create</b><i> (int&nbsp;<var>fd</var>, const&nbsp;char&nbsp;*<var>filename</var>, ttyctl_t&nbsp;<var>tty_control</var>, const&nbsp;char&nbsp;*<var>css_filename</var>)</i>
<a name="IDX48"></a>
</dt>
<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>,
styled with the file <code><var>css_filename</var></code> if possible.
</p>
<p><code><var>filename</var></code> is used only for error messages.
</p>
<p><code><var>tty_control</var></code> specifies the amount of control to take over the
underlying tty.
</p>
<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
closed.
</p></dd></dl>


<a name="The-html_005fstyled_005fostream-class"></a>
<a name="SEC33"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC33">3.5.4.2 The <code>html_styled_ostream</code> class</a> </h4>

<p>The <code>html_styled_ostream</code> class supports styled output to any
destination, in HTML syntax.  Its type is &lsquo;<samp>html_styled_ostream_t</samp>&rsquo;.
It is a subclass of &lsquo;<samp>styled_ostream_t</samp>&rsquo;.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> html_styled_ostream_t <b>html_styled_ostream_create</b><i> (ostream_t&nbsp;<var>destination</var>, const&nbsp;char&nbsp;*<var>css_filename</var>)</i>
<a name="IDX49"></a>
</dt>
<dd><p>Creates an output stream that takes input in the UTF-8 encoding and
writes it in HTML form on <code><var>destination</var></code>, styled with the file
<code><var>css_filename</var></code>.
</p>
<p>Note: The resulting stream must be closed before <code><var>destination</var></code>
can be closed.
</p></dd></dl>


<a name="The-noop_005fstyled_005fostream-class"></a>
<a name="SEC34"></a>
<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC34">3.5.4.3 The <code>noop_styled_ostream</code> class</a> </h4>

<p>The <code>noop_styled_ostream</code> class supports the styled output operations
to any destination.  The text is output to the given destination; the
styling operations, however, do nothing.  Its type is
&lsquo;<samp>noop_styled_ostream_t</samp>&rsquo;.  It is a subclass of &lsquo;<samp>styled_ostream_t</samp>&rsquo;.
</p>
<p>It can be instantiated through this function:
</p>
<dl>
<dt><u>Function:</u> noop_styled_ostream_t <b>noop_styled_ostream_create</b><i> (ostream_t&nbsp;<var>destination</var>, bool&nbsp;<var>pass_ownership</var>)</i>
<a name="IDX50"></a>
</dt>
<dd><p>Creates an output stream that delegates to <code><var>destination</var></code> and
that supports the styling operations as no-ops.
</p>
<p>If <code><var>pass_ownership</var></code> is <code>true</code>, closing the resulting
stream will automatically close the <code><var>destination</var></code>.
</p>
<p>Note: If <code><var>pass_ownership</var></code> is <code>false</code>, the resulting stream
must be closed before <code><var>destination</var></code> can be closed.
</p></dd></dl>


<a name="Debugging-the-styling-code"></a>
<a name="SEC35"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC35">3.6 Debugging the text styling support</a> </h2>

<p>If you want to understand which output of your program is associated with
which CSS classes, the simplest way is as follows:
</p>
<ol>
<li>
Run the program with the command-line option <code>--color=html</code>,
redirecting the output to a file.
</li><li>
Then inspect this output.  Text regions associated with a CSS class are
surrounded by <code>&lt;span class=&quot;<var>css-class</var>&quot;&gt;</code>...<code>&lt;/span&gt;</code>.
</li></ol>


<a name="What-to-document"></a>
<a name="SEC36"></a>
<h2 class="section"> <a href="libtextstyle_toc.html#TOC36">3.7 Documenting the text styling support</a> </h2>

<p>To make the text styling support available to the end user of your
package, the following need to be documented:
</p><ul>
<li>
The command-line options.  This typically needs to be done in several
places: in the &lsquo;<samp>--help</samp>&rsquo; output, in the <code>man</code> pages (if present),
and in the documentation.
</li><li>
Which programs support &lsquo;<samp>--color=test</samp>&rsquo;?
</li><li>
The list of CSS classes and their meaning.  This is necessary, so that
the user can create their own style file; the CSS classes are part of the
selectors in the CSS rules.
</li><li>
The location of the default style file.  This is a convenience, so that
the user, when creating their own style file, can start from the default
one.
</li><li>
The environment variable, called <code><var>style_file_envvar</var></code> above,
that, when set to a non-empty value, specifies the style file to use.
</li></ul>


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